Magnetic alloy



May 5,v 1931. l H. F. PORTER 1,303,353

MAGNETIC ALLOY Filed Jan. 20,7192? VOLTA 6'5 AHH/FICA p ma :u 4 s wu Frequency L/Mes or Wafer/on INVENTOR.

Hi f @r4/L S BY QM VOL f6 ATTORNEY.

i V.Patented May 1931 PATENT oFFlcE HARRY F. PORTER, F TRENTON, NEW JERSEY MAGNETIC ALLOY Application led annary 20, 1927. Serial No. 62,245.

My invention relates to magnetic alloys.

The `known magnetic elements and alloys` are not suited to meet the widely varying and exacting requirements oi? different types of electro-magnetic apparatus especially those in which high permeability and low .hysteresis losses are desired throughout a range extending from very low induction to airly high densities andimore particularly 1f in those cases inwhich a high and substantially constant rate of change of erineability is desired when an alternating i ux is superimposed -on a relatively large biasingmag neto-motive force. A 1,5 `For an explanation of my invention, reference is made to the accompanying drawing in which i Fig. 1 is an elevational view, partly in section, of a transformer having a solid core.

Fig. 2 is a sectional view taken on line 2 2 of Fig. 11 M Fig. is a reproduction o'-a microscopic .photograph-of the cross-'sectionfof a metal strip or lamination made according to my invention. Fig. 4 is a schematic wiring diagram of a radio receiving circuit.

Figs. 5 to 7 are various characteristicsy curves involved in the explanation of the invention.

. In my researches, I have found that a magnetic alloy may be made of copper, nickel and iron within the limits of Per cent 'Copper '.--.1 3-10 l Nickel -55 I1"onv 35-55 which in certain fields of application is-electrically and magnetically superior to known magnetizable substances and possesses` the l'additional mechanicalv advantage of` being easilyworked, as is hereinafter more. fully described.

The preferred method of lmaking this ternary alloy consists ofplacing a quantity of manganese or man anese and magnesium VVin"thebottbmrogfthe silica or quartz crucible of an induction furnace and superimposing upon it the proper proportion of copper. In

'and should be preferably bel-ow .05%.

lieu of this arrangement, an alloy (b) oi copper and manganese, or of copper and magnesium, or oi' copper, manganese and magnesium, is employed. ln any case, the iron and nickel, preferably in the form of sheets alternately arranged, are placed abovethe copper mixture or alloy so that the latter, which melts first, in eifectforms a solvent in whichthe iron and nickel dissolve. The downward movement of these melting metals and 'the currents induced by the primary windingof the furnace cause -a stirring -action'which resultsin a uniform mixture of the metals throughout the entire mass.

To obtain the desired magnetic properties of the alloy, the total carbon content should not exceed .l of 1% by weight of the allo JLD making the alloy the nickel should contain but littlecarbon, less than 005%. Electrolytic nickel may be used. Manganese onehalf of 1% insures removal of sulphur from the nickel and also de-oxidizesit. The iron should be of high purity, containing from `but .01% to .03% carbon. The copper, which may be of the usual commercial varieties, is of high oxygen content and refines `from the iron the small traces of carbon that may be present. By arranging the materials in the furnace as described, the melting and refining operations proceed simultaneously.

Thealloy should be poured soon after the entire mass has become molten; otherwise gases are formed which produce porous bars or castings.`

For the combination of Lll/2% nickel, itil/2% iron and the balance of copper, except for sm'all amounts of manganese, magnesium andtraces ofthe usual impurities,

the melting point of the alloy is about 1300 centigrade and the time of melting a charge depends, of course, upon the amount of material, and other variables.`

The alloy may be cast in various shapes,

b the use .of cast iron or sand moulds and t ereafter-machined. After all ofthe mechanical operations have been performed, the

casting are annealed ina reducing'or neutral vsiredmagnetic characteristics. The metal before annealing is, to all practical purposes,

y non-magnetic.

The castings maybe annealed in air if the precaution is taken to cover them with some substance such as iron borings, to remove impurities from the furnace gases before they come in cont-a'ct'with the casting.V Further, durin the cooling down in the open air, a partia vacuum is produced, sucking in air, which, exce t for the presence of the lter, as of iron orings, would oxidize the castings. As a matter of fact, the results produced by surrounding the casting with iron filings and annealing 1n air are fully as satisfactory as those produced by annealing in an atmosphere of hydrogen, which is considerably more expensive than the iron filing anneal. The h drogen anneal is very commonl used or highly sensitive magnetic meta or allo s having no cop er in their composition. n general, the hi er the tem-` erature at which the annea ing is perormed within the range given, the less the time required to attain the desired objective.

The magnetic characteristics of the alloy are such that when a 'casting of the metal 1s used as a core or other magnetic element in 'Ecora sultin electro-magnetic devices and the like, as

transformers, alternating current relays, its

rformance compares favorably with a lammated core of the usual known magnetic alloys as silicon-steel. The simlllicity of assem ly and construction of suc devices refrom the use of cast members'A of my alloy 1s illustrated by Fig. 1 which discloses an audio-frequency transformer, used to couple the successive stages of an audio-freacore consisting of e middle leg of the merely two castings.

vE shgapecastin- 1 receives the primary 4 of relativel few turns of wire u on which-is wound e seconda 5 of a re atively large number of turns of er wire. The magnetic lcircuitsare completed b the yoke member 2, also a casting fastene to the main member as by screws 3, passing throu h the oke and threaded into the, leg mem rs o the Instead of casting the metal in molds substantially of the shape and size of the finished product 1t may be poured in fiat slabs-similar to' theA practice emlpllpyed with non-ferrous metals prior to ro The bars or slabs are ve malleable, an may be either hot or cold ro ed, preferably cold rolled so as to reduce/to a mlmmum the absorption of car bon, oxygen or sulphur during the rolling,

inasmuch as any of lthese impurities are detties of the alloy. is almost imposi l le to alloy is much greater than in ordinary maglao i rimental to the final desired magnetic uali- Lacasse safeguard against this poisoning of the metal during the`much more involved and expensive hot rolling process which is employed with the known magnetic substances. The cold rolling also effects a change in the internal structure ofthe alloy such that an examination under the microscope of a crosssection of the cold rolled metal reveals a series of minute, finely separated lamin" completed, the strips are annealed as previously described. The tendency of light strips to stick together dwring'the annealing process,'if stacked and subjected to temperatures `in excess of 925 C. may be minimized by giving the strips a light surface oxidation prior to annealing. When annealed in a reducing atmosphere, the material assumes a highlustre and when air annealed takes on an o'xide coating desirable for transformer or other construction in which a core is .built of a pile of laminations.

The allo may also be poured inround ingots, whic are readily drawninto a wire which in turn may be drawn downto the finest sizes After annealing, the wire may be insulated and employed in circuits, as radio frequenc circuits, wherein hi hA permeability and ow losses at feeble in uctions are desirable. If cold drawn, the rod or Iwire is striated, and is, in eiect,va bundle of ,ver fine, substantially parallel wires or rods.

he ma etic properties of the alloy render it particu arl useful in electro-ma net-iedevices involved1 in the transmission o of sound frequency, such as for example audio-.transformers and im edances, having currents l a magnetic member-or mem ers subjected to O an alternating flux whose frequency may vary from 10 to 10,000 cycles per second, super-` imposed upon a relatively magneto-motive force.

Referring to Fig. 6, the curves C and D represent the general shape of the'permeabilit}1 large biasing curves oflan ordinary magnetic alloy, as sil1 con steel, and of my copper-nickeliron alloy.v respectively. The stee'pness of the linear part of the curve D, that is, the portion of c urve between 22 and 24, which may be mathematically expressed as lthe first derivativeo the permeabilityor B/H curve or dB/dH is greater than the slope of the correspondin art of the curve C between the points 22 and 3. Therefore, for values ofrmagnetizing forces H between 22 and 24 the rate of change of induction in the nickel-iron-copper alternating flux is imposed on a biasing mag-` .neto motive force, further description will be limited, for the purpose of illustration, to its use as the core member of an audio-frequency transformer having its primary in the output or plate circuit of a thermionic valve, particularly of a valve forming a part of a radio receiving set. For the sake of brevity in the description and claims, the term transformer is us'ed in its generic sense and includes transformers Whos-e vwindings are conductively or inductively coupled.

Referring to Fig. 4, 6 represents an antenna or equivalent absorption structure connected to one terminal of the primary 7Jof aradio frequency transformer Whose other terminal is connected to the ground or its equivalent 8. Placed in inductive relation to the coil 7 is the secondary 9 tuned by the variable condenser 10 and having its terminals connected to one common connection of the grid condenser 11 and grid leak 12 and to filament 13 of a thermionic valve.. The temperature of the filament or cathode is regulated by avariable resistance or rheostat 14 connected in series with' the cathode and the battery A. The control 'electrode or lgrid 15 is connected to the other common terminal of the grid leak and grid condenser.

One terminal of the primary 16 of the trans-y former T is connected to the plate or anode 1-7 of the thermionic tube and the other terminal is connected to an intermediate positive electrode of the battery B. The plate or anode circuit is completed by a conductor from the negative electrode of the B battery to the filament circuit and byv the electronic discharge from the heated cathode to theplate. The terminals of the secondary 17 `of the transformer are connected respectively to the grid 18 of a second thermionic valve and to the negative terminal of a variable, biasing or C battery. 1f an auto-transformer is used, a blocking'condenserand a grid-leak Will be employed in the controlcircuit of the second valve as is Well understood. The' the grid is at Zero potential, there is a current of 3 milliamperes flowing in the plate circuit Which subjects the core 21 of the transformer T to a definite magneto motive force. From 2 to plus 2 volts, the linearity of the curve is pronounced and is such that the change of plate current is substantially proportional to the grid volts applied. For detection or rectification, the valve would operate on the linear portion of the curve which it should be understood is not necessarily an actual curve but only representative for the purposes of explanation.

Knowing the current, by measurement, values through which the plate current passes due to measured variations of potential of the grid, it is necessary to employ a number I of turns for the primary 16 of the transformer such that only the linear portion of the permeability curve of the core is utilized, for example, from 22 to 23 of curve C if of silicon steel or from 22 to 24 of curve D if of my co er-nickel-iron alloy.

aving so designed the transformer thatthe core is always magnetized Within the rangev of linearity, the material having the steepest permeability curve, that is, the great- 'est rate of change of induction, or mathy vematically expressed, the largest dB/dI-I, is

desirable as will appear.

Delivery of energy from the thermionicy l valve to the transformer is efficient and effective for frequencies for which the primary impedance of the transformer is greater, at least 300%, than the impedance vof, the tube, a

property determined by its construction. The;

primary impedance of the transformer may be expressed by the formula Z=primary impedance f=trequency of alternating component in` cycles per second L=imsgce of primary to alternating component in cycles per As the inductance L is determined by the chan of number of lines of magnetic induction or a unit change of current in the Winding and the rate at which the lines of induction increase ordecrease simultaneously/With current changes depends upon the ZB/ZH of the medium in which they are produced, that is, the transformer laminations in fthis instance, it appears that for a given number o turns, the primary impedance is directly pro' portional to the ZB/ZH characteristic of the core material for a given frequency, and the higher thedB/ZH characteristic, the lower is the frequency for which the primary impedance exceeds by a proper percentage the tube impedance. Therefore any improvement in the dB/dH coeflicient of the magnetizable material of the transformer ismanifestedby a kgreater over-all amplification and a general improvement in tone vquality or timbre `befcause of the relatively greater amplification of low frequency tones which are Weakest When amplied by a transformer of orf dinary construction and proportions.

By using my ternary alloy, a very high primary inductive reactance impedance can be obtained with a relatively small number of primary turns so that it is possible to have an eiiicient, high impedance transformer without an excessively large number of secondary turns. It is noted that when high ratio transformers having a core of ordinary transformer iron, a primary of proper impedance, and ksecondary of a large number of turns, are used; the higher frequencies are 1 slighted due to the by-passing effect'of the large distributed capaclty of the secondary winding. If the number of secondary turns is reduced to avoid this effect, the amplification of the entire range is proportionately decreased. The ampliiicatlon curve E of a transformer using ordinary transformer iron falls off rather rapidly at each end. If the transformer is of the high impedance type and'of generous proportionsvto secure better amplification at the lower frequencies, the curve drops off more sharply at the high frequencies, as explained, and vice versa. 1n other words, the curve E may be shifted somewhat along the horizontal axis but its lshapel remains substantially the same so that its tone range is not increased but merely displaced along the frequency scale. When'a core of my coppernickeliron alloy is employed, the. amplification curve F ofthe transformer is not only. generally higher but ,is also lifted at both ends as compared to curve E sothat the effective tone range of the transformer is greatly increased, an important factor when the faithful reproduction of tones is desired.

f Other and varied uses of the alloy are suggested by its characteristics. As it is highly perme ble and productive of but low losses at very ow induction, it is adapted for use fo in current transformers, for measuring instruments as ammeters, wattmeters and watt hour meters, andv as'pole tips, armatures or other parts of devices as loud-s eakers. Its high vpermeability bat fairly 'hlgh densities makes its use desirable in. potential transformers for use with volt-meters, wattmeters,l

watt hour meters, and the like.- In ignition apparatus, in auto-horns, or in vibrators' generally, thelow retentivity of the alloy rec. 5 ommends its-use. It may be used as the magnetic vane of alternating current ,devices as indicating instruments, where low hysteresis losses are-desirable.

What'I claim as my invention is:

v 1. A magnetic allo'y comprising copper 3% to 10%, nickel 35% to 55% and iron 35% to 55%. a 'l 2. A inagnetizable lamination having low eddy current losses comprising a cold rolled -00 strip of'alloy of copper, 1ron and nickel.

a 3.'An electro-magnetic device 4comprising coil structure, and core structure therefor of a magnetic alloy comprising copper 3% to "'"IO%, nickel 35%Y to 55%'and iron 35% to 4. An electromagnetic device com rising coil `structure traversed by current aving alternating and direct current components, and core structure therefor of a ma ectic alloy comprising copper 3% to 10%, nickel 35% 7o to 55% and iron 35% to 55%, and of solid cross-section.

5. A transformer having a secondary Winding and a primary winding traversed by current Whose direct current component is large relative to the alternating current component, and core structure therefor of a magnetic alloy comprising copper 3% to 10%, nickel y35% to 55% and iron 35% to 55%.

6. A transformer having a secondary Windo ing and a primary Winding traversed by current whose direct current component isylarge .relative to the alternating current component, andcore structure therefor of solid cross-section and of a magnetic alloy comprising copper 3% to 10%, nickel 35% to 55% and iron 35% to 55%.

7. A magnetic alloy comprising commercial copper 3% to 10%,' nickel 35% to 55% and iron 35% to 55% containing carbon less 90 lthan .03%. a i

8. An electro-magnetic device comprising a winding traversed by current having alternating and direct lcurrent components of which the direct current component is large relative to the alternating current component, and core structure of high initial permeability, unsaturated by said direct current component, composed of a mafrnetic alloy comprising copper 3% tb 10%, nickel 35%to 100 55%, andiron 35% t0 55%. A

9. A transformer having a' winding traversed by current having alternating and direct current components of which the direct current component is large relative to the alternating current com onent, and core structure 4therefor having iigh initial permeability, unsaturated by said relatively lar e direct current component, composed of an a loy comprising copper 3% to 10%, nickel 35% 110 to 55%, and iron 35% to 55%. L i 10. An audio-freueney transformer. hav-1 ing'a primary Win ing traversed by a curr. rent having'a sound-representing component and v a direct rcurrent component relatively large with respect to said sound-representing current, and .core structure therefor, un,- saturated by said relatively large direct current component, compose of an alloy comprising copper 3% to 10%, nickel '35% to, 1an

55%, and iron 35% to 55%. l HARRY F. PORTER. 

